Question

Calcule a soma dos 30 primeiros termos da PA (-15 , -11, -7, ...)​

Answer 1

Resposta:

Explicação passo-a-passo:

r = a2 - a1

r = - 11 - ( - 15 )

r = 4

a30 = a1 + 29r

a30 = - 15 + 29 * 4

a30 = - 15 + 116

a30 = 101

Sn = ( a1 + an ) n / 2

Sn = ( - 15 + 101 ) 30 / 2

Sn = 86 * 15

Sn = 1290

Answer 2

$\large\boxed{\boxed{\boxed{{Ol\'a\:Anne\:Gabriely}}}}}$

$\large\boxed{\boxed{{a_{n}=a_{1}+(n-1)r}}}}}$

Onde:

$a_{1}=-15$

$n=30$

$r=a_{2}-a_{1}=-11-(-15)=-11+15=4$

$a_{n}=a_{30}=??$

Substituindo teremos:

$a_{30}=-15+(30-1).4$

$a_{30}=-15+29.4$

$a_{30}=-15+116$

$a_{30}=101$$\checkmark$

$\large\boxed{\boxed{{S_{n}=\frac{a_{1}+a_{n}}{2}.n}}}}}$

$S_{30}=\frac{-15+101}{2}.30$

$S_{30}=\frac{86.30}{2}$

$S_{30}=\frac{2580}{2}$

$\large\boxed{{S_{30}=1290}}}}}$

$\underline{Qualquer \:D\'uvida\:Comente}$